Fluororesins have been widely used in the fields of kitchen utensils such as frying pans, pans, hot plates, inner pots for rice cooker-warmers, etc., food containers, electric appliances, food industry, electrical industry, engineering industry, etc., because they are excellent in non-tackiness and chemical resistance. The coatings of conventional fluororesin-coated materials are mostly transparent so that the colors of substrates are seen through the coatings, or the colors thereof are mainly monotone such as white, gray or black. Only metallic tones can be obtained at most by imparting metallic luster thereto even if they can be colored.
However, the needs of the colors of general-purpose goods, particularly-household articles, have been increased in recent years. For example, refrigerators which allow colors thereof to be ordered are on sale. That is, colors which have been conventionally considered as a secondary function are made to be an essential element.
Fluororesins have excellent chemical resistance and are not dissolved in most of solvents. Conventionally, aqueous dispersions of fluororesins or powders thereof have been coated on materials and then backed at a high temperature to produce coated materials. Hence, organic coloring materials such as dyes could not be used because they are denatured by heat. On the other hand, when the fluororesins are colored with inorganic pigments such as red iron oxide and ultramarine, there are disadvantages that when small amounts thereof are used, a sufficient color cannot be formed, while when large amounts thereof are blended, important functions such as surface non-tackiness, etc. are greatly deteriorated.
When the inorganic pigments are used in a relatively small amount which do not damage the important factions, only monotone color such as white, gray or black can be obtained by blending carbon black or titanium oxide capable of forming a good color by harmonizing with the colors of substrate materials.
Mica, which has provided satisfactory results for many years as sliding materials, is blended with fluororesin compositions to be coated on articles which require wear resistance, such as frying pans, so as to improve the wear resistance, and a metallic color tone is obtained as a secondary effect. However, when only mica is blended, the hiding power of mica as a pigment is poor, and hence considerable non-uniformity in color is produced by the unevenness of the thickness of coating. Accordingly, metallic powder, silica, alumina, carbon or titanium oxide is commonly used in combination with mica.
Such combinations are described, e.g., in JP-A-52-10386 (the term "JP-A" as used herein means an "unexamined published Japanese patent application), published PCT Patent Application (Japan) No. 56-501277 and JP-A-56-103256. There are disclosed that metal flakes, mica or pigment-coated mica is blended with fluororesins in order to improve coating strength such as scratch resistance and wear resistance, without the exception that metallic powder, silica, alumina, carbon or titanium oxide in an amount commonly added is used in combination therewith so as to prevent non-uniformity in color from being caused. Further, the addition of a heat-resistant high-molecular material is often essential.
In JP-A-52-10386 and published PCT Patent Application (Japan) No. 56-501277, non-tackiness inherent in fluororesins are greatly deteriorated because such additives are employed. Therefore, the necessity to provide a top coat composed of only a fluororesin or a top coat containing a reduced amount of mica on the surface arises, or it is necessary that the use of such blends is limited to only a subbing layer for the coating of fluororesins as described in JP-A-56-103257. With regard to color tone, only monotone type metallic color is obtained at present because the amounts of pigments to be blended are limited to a certain range in order to minimize a lowering in adhesion to the substrate and non-tackiness as similar to the case of the compositions containing no mica.
Attempts to improve wear resistance have been made by the structure of coating. For example, an improvement in wear resistance has been made by coating a primer containing a heat-resistant high-molecular weight material on a metallic substrate and then coating a fluororesin composition containing mica thereon. This is because the high-molecular weight material contained in the primer is firmly bonded to the substrate and an effect of greatly improving wear resistance is exhibited by a synergistic effect with mica coated thereon. This technique is a conventional method which is applied to most of commercial available articles of fluororesin coated materials which require were resistance at present. However, only monotone type metallic color is obtained as described above.